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arXiv · 2608.10165

The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) Survey: A Molecular Gas Line Search

V. Catán·J. González-López·M. Aravena·A. S. Long·C. M. Casey·D. L. Clements·E. da Cunha·M. Franco·A. M. Koekemoer·A. Man·J. Spilker·E. Treister
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Abstract

Current investigations of cold gas in the interstellar medium face selection biases, as optical/near-infrared surveys favor massive, low-obscuration galaxies and miss gas-rich passive or inefficient star-forming systems. Overcoming this requires large-volume line surveys selected by molecular gas rather than stellar luminosity. We present a molecular gas census across $0.5 < z < 5$ using ALMA Band 4 observations from the Extended Mapping of Obscuration to Reionization Survey (Ex-MORA), covering 577 arcmin$^2$. Combining an unbiased search for bright emitters with a targeted search using spectroscopic redshift priors, we detect 52 galaxies in CO or \ci transitions (two showing two lines). Physical properties were derived via \texttt{CIGALE} with non-parametric star-formation histories, and gas masses were estimated using metallicity-dependent conversion factors. The sample is dominated by main-sequence (MS) galaxies with high stellar masses (median $\log M_*/\text{M}_{\odot} = 10.83$) and large gas reservoirs ($>10^{10}\,\text{M}_{\odot}$). Gas fraction ($\mu_{\text{gas}}$) increases with redshift for active populations, though high-redshift trends are influenced by a gas-rich protocluster at $z \approx 2.4$. Conversely, an overdensity at $z \approx 0.73$ mirrors the field population. Five Green Valley (GV) galaxies exhibit a $\mu_{\text{gas}}$ peak at cosmic noon, suggesting stellar feedback may suppress star formation by heating gas rather than rapidly depleting it in at least some transitional systems. Resolved kinematics show a prevalence of rotating disks. These results demonstrate that wide-area line searches effectively recover massive gas reservoirs across diverse evolutionary stages

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V. Catán, J. González-López, M. Aravena, A. S. Long, C. M. Casey, D. L. Clements, E. da Cunha, M. Franco, A. M. Koekemoer, A. Man, J. Spilker, E. Treister. 2026-08-10. The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) Survey: A Molecular Gas Line Search. https://arxiv.org/abs/2608.10165

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